Btw schools have to manage the behaviour of 1000+ teenagers in crowded conditions from very different backgrounds and manage to give those kids an education.
What seem like petty rules to you are the backbone of creating a culture in which kids can actually learn because they have accepted some common, simple boundaries and respect for the culture of the school.
If you can't even get one child, your own child, to follow a simple instruction then imagine the challenge of getting over a thousand of them to follow rules that will keep them safe and allow others to learn even if they don't want to themselves and tell you, 'their parents don't give a shit either'?
Well researched strategies and systems are put in place and it turns out, mad or not in my or your opinion, that getting kids to accept and adhere to low level simple rules of conformity such as uniform are key. You might want to also consider that if your dd is being sent to the pastoral office to sort out the fact she's wearing earrings again and has already been warned and now has to do x, y or z, she is NOT in her lesson learning as she is meant to be. She may well have also robbed her whole class of five minutes learning whilst the teacher 'persuaded' her that yes she really did have to go to the pastoral office seeing as she'd chosen to disregard the rules again and no we don't have time during our maths lesson for a one on one argument about whether she should have to follow rules or not because there are 29 (or god forbid 32) other kids in that room whose parents have sent them into school to get an education not listen to this.
If you deal with it at home it is just you who has to waste your time arguing and enforcing - if you say, 'let the school deal with it' because I can't be bothered then it impacts on a lot of people including the the kids of the parents who could be bothered having that battle at home out of consideration for the rest of the community.
If you hate the rule then complain about it, talk to other parents, write to the board of governors etc. At my school they're allowed one plain stud in each ear and one small nose stud. So there's your first argument for your case: many schools allow..... can I ask why you don't follow a similar policy? Petition, lots of emails from parents etc. The, 'this is a stupid rule', is a red herring because you could challenge the rule constructively in an adult way.